The invention relates to an apparatus which can be attached to a pressurized water bearing hose to generate foam, in particular to an apparatus for attachment to a fire fighting hose to generate fire fighting foam from a supply of pressurized water as used in fire fighting.
While water is used for many fire fighting applications, when the water is mixed with a small amount of foam concentrate or foaming agent and passed through a suitable foaming nozzle, a large volume of foam can be generated. For many common fire fighting applications e.g. Class A fires involving wood, paper etc., foam is considerably more effective than water by itself. Also for special fire fighting situations e.g. Class B fires involving liquid fuels, combustible solvents etc., water by itself cannot be used, and thus foam, dry powder or gaseous extinguishers must be used. Foam is usually necessary for large Class B fires, as the other methods are too costly or not practical.
Foam can be applied on a fire from two sources, namely from a pressurized canister source, or by adding foam concentrate to a stream of water under pressure. The first source of foam applying equipment is limited for use on small fires only, due to its small capacity which is usually limited to the size of canister that can be easily handled by one person. The second source of foam applying equipment is commonly mounted on a fire truck to facilitate transport to a site. The second source of foam applying equipment is described herein and comprises a foam concentrate metering and mixing device for adding to pressurized water from a hydrant or to another pressurized water source. The mixture of pressurized water and foam concentrate must be passed through a suitable nozzle to generate foam, the nozzle also providing a means of mixing air with the water and foam mixture so as to generate a suitable continuous supply of foam. Where water is not pressurized, a water pressurizing device such as a pump is used to raise water pressure, often concurrently with adding a metered amount of foam concentrate to the water stream. The foam concentrate can be introduced to the water stream at the truck itself, in which case the foam concentrate is simultaneously mixed and fed along the hose, and is then discharged at the source of fire. If the foam concentrate is fed along a sufficient length of hose, there is usually no difficulty in mixing the concentrate with the water, so that when the foam water mixture passes through the foaming attachment on the nozzle, a good supply of foam is generated.
One disadvantage with introducing the foam to the hose pipe at the truck is that the hose pipe is then somewhat limited to delivering only foam, and cannot be quickly easily changed to delivering water, at least not by the person directing the hose. Relatively complex machines that resemble the first type of foam generating devices are shown in U.S. Pat. Nos. 4,645,009 (Hawelka et al.) and 3,234,962 (Williamson). Such machines can be relatively costly and this detracts from their use.
Alternatively, the foam concentrate can be fed in a separate concentrate hose extending along the main water hose to an eductor nozzle located at a position in the hose, suitably some distance from the discharge nozzle to permit adequate mixing of the foam concentrate with the water prior to discharge. This method has a disadvantage of having two parallel lengths of hoses for at least a short length of the water hose, with a separate control on the foam concentrate hose to control supply of the foam concentrate. A simple means of metering foam concentrate into a water stream is shown in U. S. Pat. No. 4,993,495 (Burchert) in which water passes through a venturi means and generates suction to draw foam concentrate into the water flow. With this alternative device, there must be sufficient length of hose downstream from the venturi means to provide adequate mixing of the concentrate and foam before the mixtures passes through a nozzle to generate foam. A nozzle to generate foam from a water and foam concentrate mixture is shown in Canadian Patent 1,266,073 (Stevenson). Such a nozzle requires to be supplied with a mixture of water and foam and thus requires at least a foam concentrate metering and mixing structure upstream of the nozzle which structure is usually provided at the fire tank or in the length of the water hose.
An apparatus which combines metering and mixing of foam concentrate essentially integral with a foaming nozzle is shown in U.S. Pat. No. 2,513,417 (Lindsay). This patent shows an eductor nozzle structure for drawing foam concentrate into a stream of water prior to ejecting the resulting mixture through a foaming nozzle which draws in air to generate foam. This is a relatively complex mixing nozzle with an annular gap located downstream of a converging section for drawing foam concentrate into the water, followed by a constant cross-section portion with a conical spreader which separates the stream of mixture in an air entrainment chamber. A further teardrop-shaped baffle is required to control velocity of the fluid to achieve a more uniform foam quality.